A variety of different battery-operated tools and other consumer products currently are available on the market. Typically, these products are powered by rechargeable batteries or rechargeable battery packs. Devices of this type include portable battery-powered electric drills and screwdrivers, VCR cameras, cellular telephones, and the like. Some such devices, such as portable hand tools, generally build the rechargeable battery into the tool. When the tool is not in use, it is placed on a charging stand connected to a source of charging current, to recharge the battery between uses. Operation of the tool always is from the battery, and operation of the tool is not intended when the battery is being charged.
VCR cameras and cellular telephones typically employ removable batteries or battery packs. Such cameras and cellular telephones are operated from the batteries, and the batteries generally are removed from the devices and placed in a charger (either a "trickle" charger or a fast charger) to recharge the batteries between uses. Users of such devices generally have two or more batteries, one of which is in the charger and the other of which is in the device. Consequently, when a battery becomes discharged, it is removed from the camera or telephone and replaced with the battery which was being charged. The depleted battery then is placed on the charger, and this cycle is repeated. Obviously, this requires a number of separate items, including the extra batteries or battery packs, since a single battery pack is not sufficient if continuous use or long-term use of the camera or cellular telephone is desired.
Some cellular telephones also include a power convertor that can be used in place of the battery pack to operate the telephone. Typical of such power convertors are a battery eliminator pack, which plugs into the lighter socket or some other source of supplemental power within an automobile, and is attached to the cellular telephone in place of the battery pack. Thus, the battery pack then may be placed in a battery charger, to charge it up and maintain the charge until it next is needed. Currently available battery eliminator devices of the type which plug into the electrical output of an automobile are removed from the cellular telephone and replaced with a battery pack whenever the cellular telephone is to be used in locations other than the automobile. Cellular telephones, in addition, currently are designed such that the battery cannot be fast charged while it is attached to the telephone.
Cordless telephones, primarily designed for household use, include a base station and a portable handset. When the handset is not in use, it typically is placed on the base station; and contacts are provided to charge the rechargeable battery mounted within the handset; so that it is ready for operation as desired. Several patents directed to cordless telephones employing this basic feature are Luce U.S. Pat. No. 3,919,491; Yamazaki et al U.S. Pat. No. 4,511,761; Grassl U.S. Pat. No. 4,634,810; Kato U.S. Pat. No. 4,726,052; and Makino U.S. Pat. No. 4,939,770.
The patent to Steinbeck U.S. Pat. No. 4,752,949 is directed to a telephone which is capable of operation in either a cordless or corded mode. The portable handset used in both of these modes includes a battery which is only charged when the handset is placed in an "on hook" condition. This is a standard mode of operation for household cordless telephones. The unit, however, also includes an automatic switch-over from cordless to corded operation whenever the cord is plugged into the handset portion. No charging of the battery takes place in this mode, which is similar in some respects to cellular telephones which can be operated either from a battery or from a supplemental power source.
The Bolgiano U.S. Pat. No. 4,272,650 is directed to a portable telephone system. The configuration for the telephone includes a power supply network having a primary high voltage power source (an external battery) which normally operates the telephone. When this external battery power source is connected, the operation of the telephone is effected in its normal manner. In addition, however, a secondary, low voltage battery is continuously charged by the primary higher voltage power source battery. When the primary power source is removed for replacement or recharging, the secondary, low voltage battery provides power to a portion only of the circuitry of the telephone. The telephone unit itself, however, cannot be operated by the secondary power source alone.
It is desirable to provide a power pack unit for operation with battery-operated devices, such as cellular telephones, which simultaneously powers the telephone, or other devices, and supplies charging current to the battery when supplemental power is connected, while automatically causing the telephone to be operated from the battery, when supplemental power no longer is connected.